BOHALLER. 
DUMORTIERITE. 95 
locality. About 25 specimens are shown, the best one containing a 
prismatic group of fine blue dumortierite libers 5 cm. long and from 
one-half to 1 cm. thick. The rock is a pegmatitic gneiss, and consists 
chiefly of quartz and feldspar, with smaller quantities of biotite, mus- 
covite, black tourmaline, dumortierite, and garnets. The dumortierite 
occurs in long prisms, often bent, and again broken, the space between 
being filled with the gneiss rock. The basal cross fracture is common 
and the color is often changed to a dull gray. At times the fibers are 
seemingly intergrown with the tourmaline in parallel position. The 
three crystals described later were obtained from these specimens. 
As additional localities, Mr. Braun gives: One hundred and first 
street and Lexington avenue, New York; One hundred and eighteenth, 
One hundred and twentieth, One hundred and twenty-second streets 
and Madison avenue; One hundred and thirty-eighth, One hundred 
and thirty-ninth, One hundred and fortieth, One hundred and forty- 
ninth streets and Mott avenue; One hundred and thirty-third, One 
hundred and thirty-fifth, One hundred and forty-ninth streets and 
Hudson River Railroad; One hundred and forty-ninth street and Sheer- 
ier place; One hundred and seventy-first street and Boulevard. 
The mineral possesses a strong pleochroism, ranging from colorless 
to deep blue, this color being always in the direction of elongation. 
The extinction is parallel and the mineral orthorhombic. Cleavage 
parallel to the macropinacoid is perfect, these cleavage plates showing 
he emergence of an obtuse bisectrix. An imperfect cleavage parallel 
to the base is also noticed, and basal sections show an imperfect pris- 
natic cleavage. Such sections show the emergence of an acute bisec- 
rix. The mineral is negative. The axial plane is parallel to the 
michypinacoid and the orientation is a=JC, b=b, c = a. The ple- 
xhroism is C=fr, colorless; 11, deep blue. Absorption, &>&=£. 
fl Some sections show polysynthetic twinning lamellae, but their relation 
ould not be made out. 
AKIZONA. 
At Clip, Ariz., dumortierite occurs in a quartz rock which has not 
een found in place (Doctor Hillebrand), but only as loose bowlders. 
|)umortierite and quartz form the principal mineral constituents, kya- 
lite, magnetite, and muscovite being present in subordinate amounts. 
he rock is fine grained and has a blue color due to the dumortierite. 
Jl Under the microscope, a section of the rock showed numerous 
mall lath-shaped prisms of dumortierite placed in every direction in 
mass of allotriomorphic quartz, with several large blades of musco- 
ite and abundant magnetite, and a little apatite and rutile. Feldspar 
hmiis to be entirely absent. 
The dumortierite has the usual colorless to blue pleochroism and 
Jjresents normal properties. In the slide studied it is very fresh and 
I hows no signs of alteration, the muscovite present being primary. 
